A search for "UK tax calculator" returns dozens of results. Most agree on the headline figures. A few differ by hundreds of pounds. The gaps usually come down to how each tool handles the trickier parts — pension contributions, student loans, Scottish rates, and adjusted net income.
This is a fair comparison of what the best-known free UK tax calculators actually do, and where they can go wrong.
What every good calculator should handle
- The correct personal allowance and taper above £100,000.
- Scottish or rest-of-UK bands based on where you live.
- Employee National Insurance at 8 per cent and the 2 per cent rate above the upper limit.
- Student loan plan 1, 2, 4, 5, and postgraduate thresholds.
- Salary sacrifice, workplace pension contributions, and relief at source versus net pay schemes.
- Bonuses and how they affect the personal allowance in a single pay period.
MoneySavingExpert calculator
MoneySavingExpert's UK Tax Calculator is one of the most popular tools on the internet. It handles the main bands, National Insurance, and student loans. It is accurate for simple salary cases but is less detailed for complex pension arrangements and does not always flag the Scottish bands clearly.
GOV.UK tools
HMRC's own tools on GOV.UK are narrow but authoritative. The Check your Income Tax service compares your tax against HMRC records and is the most accurate way to check what you have actually paid. It is less useful as a forward-looking salary planner.
YourIncomeCalculator
Our own UK salary calculator is designed to match the detail of HMRC but with a simpler interface. It handles Scottish rates, all student loan plans, salary sacrifice, adjusted net income, Marriage Allowance, and the High Income Child Benefit Charge. The results are rounded to the nearest pound, which matches the usual HMRC approach.
Our sister tax code calculator decodes the letters and numbers on your payslip and shows what they should produce in take-home pay.
How to sense-check any calculator
Regardless of which tool you use, cross-check at least three figures against your P60 or the Personal Tax Account:
- Total income for the year (should match the P60 almost exactly).
- Tax paid (should be within a few pounds).
- National Insurance paid (should match the NI letter on your payslip).
If any of those three is off by more than £20, the calculator is probably missing something — a bonus treatment, student loan threshold, or Scottish band — and you should trust the payslip or HMRC record over the calculator.
When to pay for an accountant instead
Calculators are good for estimation, not for filing. If your tax involves self-employment, rental income, crypto, capital gains, or international issues, a one-off session with an accountant usually pays for itself. Use calculators to prepare the conversation, not to replace it.
The bottom line
Most free UK tax calculators are accurate enough for salary estimation. Differences show up when pensions, bonuses, or Scottish rates get involved. Pick one tool, use it consistently, and always cross-check against your P60 and HMRC Personal Tax Account.